refactor[devtools/extension]: refactored messaging logic across different parts of the extension (#27417)

1.
https://github.com/bvaughn/react/commit/9fc04eaf3fb701cdc14f57d5aed48f3126af6c94#diff-2c5e1f5e80e74154e65b2813cf1c3638f85034530e99dae24809ab4ad70d0143
introduced a vulnerability: we listen to `'fetch-file-with-cache'` event
from `window` to fetch sources of the file, in which we want to parse
hook names. We send this event via `window`, which means any page can
also use this and manipulate the extension to perform some `fetch()`
calls. With these changes, instead of transporting message via `window`,
we have a distinct content script, which is responsible for fetching
sources. It is notified via `chrome.runtime.sendMessage` api, so it
can't be manipulated.
2. Consistent structure of messages `{source: string, payload: object}`
in different parts of the extension
3. Added some wrappers around `chrome.scripting.executeScript` API in
`packages/react-devtools-extensions/src/background/executeScript.js`,
which support custom flow for Firefox, to simulate support of
`ExecutionWorld.MAIN`.

packages/react-devtools-extensions/src/background/dynamicallyInjectContentScripts.js

@@ -13,6 +13,13 @@ const contentScriptsToInject = IS_FIREFOX
         persistAcrossSessions: true,
         runAt: 'document_end',
       },
+      {
+        id: '@react-devtools/file-fetcher',
+        js: ['build/fileFetcher.js'],
+        matches: ['<all_urls>'],
+        persistAcrossSessions: true,
+        runAt: 'document_end',
+      },
     ]
   : [
       {
@@ -23,6 +30,14 @@ const contentScriptsToInject = IS_FIREFOX
         runAt: 'document_end',
         world: chrome.scripting.ExecutionWorld.ISOLATED,
       },
+      {
+        id: '@react-devtools/file-fetcher',
+        js: ['build/fileFetcher.js'],
+        matches: ['<all_urls>'],
+        persistAcrossSessions: true,
+        runAt: 'document_end',
+        world: chrome.scripting.ExecutionWorld.ISOLATED,
+      },
       {
         id: '@react-devtools/hook',
         js: ['build/installHook.js'],